DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENVIRONMENT AS REGARDS PERCEPTION OF SCALE

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1 R. Stouffs, P. Janssen, S. Roudavski, B. Tunçer (eds.), Open Systems: Proceedings of the 18th International Conference on Computer-Aided Architectural Design Research in Asia (CAADRIA 2013), , The Association for Computer-Aided Architectural Design Research in Asia (CAADRIA), Hong Kong, and Center for Advanced Studies in Architecture (CASA), Department of Architecture-NUS, Singapore. DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENVIRONMENT AS REGARDS PERCEPTION OF SCALE Lei SUN, Tomohiro FUKUDA, Toshiki TOKUHARA and Nobuyoshi YABUKI Osaka University, Suita, Osaka, Japan sonrai@it.see.eng.osaka-u.ac.jp, fukuda@see.eng.osaka-u.ac.jp, tokuhara@it.see.eng.osaka-u.ac.jp, yabuki@see.eng.osaka-u.ac.jp Abstract. This paper focuses on differences of spatial reasoning capacity observed by using a physical model and a virtual reality (VR) system, and specifically emphasizes perception of the scale of space. While respondents viewed a physical model and a VR system, a questionnaire was used to objectively evaluate these and establish which was more accurate in conveying object size. As a result, it was acknowledged by the respondents that the physical model performed more accurately and quickly. Subject to further validation, we expect the physical model to offer great utility to develop new digital media in the future. Keywords. Spatial reasoning capacity; scale perception; physical model; virtual reality; questionnaire. 1. Introduction Aside from text and diagrams, three-dimensional visualization media, such as physical models, CG (Computer Graphics) and VR (Virtual Reality), are used to confirm space or volume in the design and presentation of architectural and urban fields (Dorta and LaLande, 1998; Belcher and Brian, 2008; Fukuda et al., 2009). The physical model and CG/VR can display in arbitrary viewpoint so that they are effective on the occasion of discussion and examination. A physical model has the advantages that several people can observe it from any viewpoint simultaneously and see the picture of a whole depicted city at once. On the other hand, there are still some difficulties if considering the pedestrian viewpoint and limits of representation caused by the small scale. CG/VR is a media using a virtual environment (virtual media) and is easy to show an eye-level viewpoint of pedestrians and drivers as well as other people and vehicles, and it can simulate such effects as solar 457

2 458 L. SUN, T. FUKUDA, T. TOKUHARA AND N. YABUKI radiation in a dynamic way. On the other hand, problems remain, such as possible viewpoints normally limited to one place and intangibility as well. Due to the distinct characteristics of the physical model and CG/VR as mentioned, they are now used together in construction sites or for planning or design (Tokuhara et al., 2010). For instance, at the stage of planning and design, a physical model is used in the first conceptual expansion phase, and then CG/VR is used in the other convergent design phase. The reasons for combining the physical model and VR, include ease of fabrication, manipulation of users, cost and labour. Meanwhile, the differences based on a physical-media model and virtual-media VR may also be a factor. Spatial reasoning capacity refers to understanding the shape, size, location and texture of an object or space. However, people have to use many clues and think carefully in order to understand it. Moreover, how to use those clues is completely unexplained, as a result of the complexity caused by distances to the object and observation conditions PREVIOUS STUDIES Siitonen (1995) used and compared a walk-through VR and an endoscope-photographing model method, and verified which one was better in manipulation, lighting and spatial reasoning capacity through visual observation of outcomes and interviews with participants. The verification results, however, lacked objectivity because they had not been quantified. In addition, as a study of spatial reasoning capacity using media systems, Witmer and Singer (1998) implemented a questionnaire on control, sensory, distraction and realism factors contributing to a sense of presence in VR. Furthermore, a new questionnaire was conducted by Lessiter and Freeman (2001) which addressed sense of physical space, engagement, ecological validity and negative effects factors. Also, spatial reasoning capacity was compared in the results from Imax2D, Imax3D, computer games and videos and calibrated principal components analysis. However, according to the above studies, the respondents, even in another scene, could still experience a sense of being there elicited by VR but can hardly do so with a real-media model PURPOSE OF THIS STUDY This paper focuses on differences in spatial reasoning capacity observed by using a physical model and a VR system, and specifically emphasizes perception of the scale of space. While respondents viewed a physical model and a VR system, a questionnaire was used to objectively evaluate these and establish which was more accurate in conveying object size.

3 DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENV Experimental Methodology The experiment showed respondents the same object that was depicted by both the physical model and VR alternatively, and required three grouped categories: the first was a height comparison of the relative size, the second was the absolute size of one building, and the third was the scale of the object. The object in this experiment was part of a shopping area (square 100m) in Buzenda, Shimonoseki City, Yamaguchi Prefecture, Japan, where there are about 30 buildings within 3~30m height on flat ground. Buildings and ground used a monochrome texture of white and grey so that it was impossible to judge the size from the building floor height or road width. A digital model for VR was created using Autodesk 3ds Max The physical model was derived from VR digital data and created by a 3D printer. 1 As a way of observation, in order to avoid bias from the respondents previous experience of VR manipulation, which could affect the evaluation, the VR camera was set up at an angle of 45-degree from the ground and captured a fly-through movie (VR movie as below) which circles around from a bird s-eye view. 2 The respondent sits at a 600mm distance from the VR display (21 inches) and viewed it horizontally. It was not expected that a respondent would look differently at the VR and physical model, so we tried to match these two media in terms of size, viewpoint angle and brightness. Al so, the physical model was mounted on a turntable that could rotate 360 degrees (Figure 1). At the beginning of the experiment, the respondents were told that the depicted physical model and VR movie content were part of one city in Japan but they were Figure 1. Position of a respondent and media (up: physical model, down: VR).

4 4B-129.qxd 4/28/ :23 AM Page 460 L. SUN, T. FUKUDA, T. TOKUHARA AND N. YABUKI not informed of its name since we wished to reduce the effects of different levels of knowledge or preconceptions related to the location at this time. The physical model and VR movie respectively span one time before the questions were presented. The first question was the height comparison of buildings. The questioner showed the physical model and VR movie in sequence and indicated two buildings with different heights in the object. The respondent was then required to answer which one is higher. In order to avoid impression change generated by pointing out the building, each media was presented from a still viewpoint. There were four pairs of presented buildings and the real height differences were 1.5m (building A: 6.5m, Building B: 5m), 5m (A: 15m, B: 10m), 10m (A: 18m, B: 28m), and 20m (A: 30m, B: 10m). Every respondent viewed the buildings at a 30degree angle. Figure 2 shows the pairs for height comparison of buildings. Figure 3 Figure 2. The building pairs for height comparison. Figure 3. Experiment image (left: physical model, right: VR).

5 DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENV. 461 Figure 4. Every viewpoint requiring the height difference. (Up: 1.5m, upper middle: 5m, lower middle: 10m, down: 20m). shows the experiment image and Figure 4 illustrates every viewpoint related to the question on the height difference. The second question was about the real size of one building. The questioner presented a physical model and VR movie in sequence and asked the responds to judge the real size of one building (see Figure 2, the building for the real size question ). Then, the respondent answered the question how many millimetres in the physical model and how many meters in the virtual space. The third question was on the scale of the physical model. As each question was answered, the response time was measured by a stopwatch until the end of the final answer. 3. Experimental Results Experiments were administered on September 24 (Saturday) ~ 30 (Friday) The respondents were a total of 24 students, and all were aged in their 20s, among which

6 462 L. SUN, T. FUKUDA, T. TOKUHARA AND N. YABUKI 16 were male and eight were female. Additionally, in order to avoid their impression being changed by the presented sequence of the media, half of the sample experienced the physical model first while the other half experienced the VR first. A five-point scale was chosen as the response option for the height comparison of buildings. 1 = A is high, 2 = A is rather high, 3 = same, 4 = B is rather high, and 5 = B is high. According to the real height difference, the correct answers were these: number 1 was assigned 1.5m, 5m, 20m and number 5 was 1m and 10m. The mean and variance of the absolute value of the difference in a correct answer and the response in each question were calculated. The response time was set as the average response time of the height comparison of buildings. To assess the real size of one building and the scale of the physical model, (i) assign H a (mm) the height on physical model, (ii) H b (m) the one on VR, and (iii) H c (m) the product of building height and scale. H was the correct answer, which was 50mm for case (i) and 25m for case (ii), (iii). The rate of deviation (see equation 1) was defined for each H a, H b, H c and H and the mean and variance of these were calculated. Exploratory analyses were performed based respectively on presented media order, respondents experience, gender as well as the sample. D x = 1 H x / H (x = a, b, c) (1) 3.1. SAMPLE ANALYSIS Table 1 shows the correctness in referring to the height comparison. First of all, everyone correctly responded to the height differences of 10m-, 20m-case on the physical model and the 20m case on VR. Therefore, in these cases, tall buildings were evaluated accurately. Then, it was clearly found that responses elicited by the Table 1. The correctness referring to the height comparison (N = 24). Height difference(m) Medium Correct Mean Mean Correct Variance 1.5 Physical model * VR Physical model ** VR Physical model ** 0 0 VR Physical model VR Non*: no statistical significance, *: 5%, **: 1%

7 DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENV. 463 Table 2. Average response time (N = 24). Height difference(m) Physical model (s) VR (s) Physical model-vr (s) ** ** ** * Non*: no statistical significance, *: 5%, **: 1% Table 3. The real size and physical model s scale based on presented media order (N = 24). Physical model (D a ) VR (D b ) Physical model scale (D c ) Average rate of deviation 22.50% 72.20% % Variance physical model are more accurate than those by VR in the case of 1.5m within statistical significance 5% (5%), and 5m, 10m within significant difference-1% (1%). Table 2 summarizes some results for response time. Timed responses to the physical model were shorter than those by VR in the case of 1.5m, 5m, 10m within 1%, and 20m within 5%. Consequently, the physical model, not VR, tends to allow quicker and more accurate comparison of building height. Table 3 indicates the results for the real size and physical model s scale. It turned out that the physical model had the lowest rate of deviation and smallest variance among respondents for three items in Table 3, namely D a, D b and D c. On the other hand, the variance in scale evaluation shown by the sample was quite large, and moreover, the value of rate of deviation in the list of physical model scale was larger than VR PRESENTED MEDIA ORDER ANALYSIS Response data divided by each height difference were entered into a t-test analysis. As shown in Tables 4 and 5, there was no significant difference in correctness or response time, which means the impression change was not related to whether a physical model or VR was used as previously discussed in section 2. The response-time difference on the other hand was small for all items if the physical model was first compared to VR. One reason for this was that the participants

8 464 L. SUN, T. FUKUDA, T. TOKUHARA AND N. YABUKI Table 4. The correctness referring to the height based on presented media order (N = 24). Mean Variance Height (Physical Mean (Physical Variance difference(m) Medium Correct model first) (VR first) model first) (VR first) 1.5 Physical model VR Physical model VR Physical model VR Physical model VR Non*: no statistical significance, *: 5%, **: 1% Table 5. Response time based on presented media order (N = 24). Height First Media Physical Physical difference(m) presented model (s) VR(s) model-vr(s) 1.5 Physical model VR Physical model VR Physical model VR Physical model VR Non*: no statistical significance, *: 5%, **: 1% grasped the whole picture during their VR experience because they had experienced the physical model before. In addition, the consequences did not vary by gender. 4. Conclusion This paper aimed to emphasize perception features of spatial scale in the spatial reasoning capacity field. It managed to assess whether a physical model or VR was more accurate and easier to use when respondents evaluated an object s size. Therefore, using a section of a city in Japan depicted by a physical model and VR,

9 DIFFERENCE BETWEEN A PHYSICAL MODEL AND A VIRTUAL ENV. 465 an experiment was conducted and 24 respondents answered questions regarding a height comparison, the real size, and physical model s scale. As a result, it was acknowledged by the respondents that the physical model performed more accurately and quickly. A comparative experiment is required to match conditions identically, except for variables. So in this study, the proposed physical model and VR were designed to be the same size and to have the same façade in order to define features of spatial dimension. To ensure they were the size same, a physical model was created from digital data by using a 3D printer employing RP (Rapid prototyping) technology. If a physical model is traditionally made by hand and VR is made by CAD separately, it is very hard to ensure they both have the same size. Therefore, information and communication technology facilitates the preparation of such environmental experiments. The future work should research the difference of size as perceived by professionals and non-professionals in architecture since citizens participation in the planning and design process has been increasing along with the use of physical models or VR on such sites. In this study, although nine of the people in the sample had some practical design experience in architecture, urban and civil engineering, this was of no special note. One of the reasons was that all respondents were students whose relative experiences was no more than three years, which was not enough to cause a difference. Acknowledgements We thank all the participants for their generous assistance in conducting the experiment. Endnotes 1. The proposed physical model was made by ZPrinter650, and had a high level of accuracy in transferring digital data to a physical model. 2. VR was performed by stereovision in the preliminary experiment (Olympus Power3D Media Player with 3D-Glass). Because the internal definition in the computer for VR was the full-size scale, the stereoscopic effect could not be seen. Therefore, stereovision was not employed in this experiment. References Belcher, D. and Brian J.: 2008, MxR: A Physical Model-Based Mixed Reality Interface for Design Collaboration, Simulation, Visualization and Form Generation, Silicon + Skin: Biological Processes and Computation: Proceedings of the 28th Annual Conference of the Association for Computer Aided Design in Architecture (ACADIA), Dorta, T. and LaLande, P.: 1998, The Impact of Virtual Reality on the Design Process, Digital Design Studios: Do Computers Make a Difference?: Proceedings of the 18th Annual Conference of the Association for Computer Aided Design in Architecture (ACADIA),

10 466 L. SUN, T. FUKUDA, T. TOKUHARA AND N. YABUKI Fukuda, T., Kaga, A., Izumi, H., and Terashima T.: 2009, Citizen participatory design method using VR and a Blog as a media in the process, Int l Journal of Architectural Computing, 2(7), Lessiter, J. and Freeman, J.: 2001, A Cross-Media presence questionnaire: The ITC-Sense of Presence Inventory, Presence, Teleoperators and Virtual Environments, 10, Siitonen, P.: 1995, Future of endoscopy updated, 2nd EAEA Conference, Tokuhara, T., Tomohio, F., and Nobuyoshi, Y.: 2010, Development of a City Presentation Method by Linking Viewpoints of a Physical Scale Model and VR, FUTURE CITIES: 28th ecaade Conference Proceedings, Witmer, B.G. and Singer, M. J.: 1998, measuring presence in Virtual Environments: A Presence Questionnaire, Presence, Teleoperators and Virtual Environments, 7,